High-performance engineering plastics having excellent heat resistance have received many attentions as advanced materials. Among such engineering plastics, poly(ether ether ketone) (PEEK), poly(ether ketone) (PEK), poly(arylene ether ketone), etc. having aromatic benzene rings introduced to the polymer chain repeatedly have been used as matrix resins of composite materials for use in airplanes and cars by virtue of their superior properties, including high mechanical strength, excellent thermal stability and chemical resistance.
However, such aromatic polymers show many problems when they are synthesized or processed at a temperature of their melting temperature (Tm) or higher due to their unique crystalline structures and low solubility. Particularly, they have poor formability into films or the like. In addition, while they have excellent mechanical properties by virtue of a high Tm of about 240° C. or higher, they are disadvantageous in that they show a rapid drop in elastic modulus near Tg because of a low glass transition temperature (Tg) of about 140-160° C. Further, they show insufficient transparency due to the above-mentioned low solubility and crystalline structures.
Meanwhile, it is known that other poly(arylene ether sulfone)-based polymers, such as poly(ether sulfone) (PES), poly(aryl sulfone) (PAS) and polysulfone (PSF) known as engineering plastics have an amorphous structure and a relatively high Tg of about 190° C. or higher. In addition, such polymers have relatively high solubility to various solvents and excellent processability and formability into films. Moreover, it is also known that films including such polymers have a relatively high transparency of about 80% or more to a wavelength of about 400-600 nm. However, since such polymers have an amorphous structure, they are disadvantageous in that they have lower mechanical properties, including mechanical strength, modulus or a coefficient of linear thermal expansion as compared to the above-mentioned crystalline polymers such as poly(arylene ether ketone).
Due to the disadvantages of such polymers, an attempt has been made to physically mix (blend) crystalline aromatic poly(arylene ether ketone) with amorphous aromatic poly(arylene ether sulfone) to obtain a composite material for high-performance engineering plastics. However, a compatibilizer having a specific chemical structure is required essentially in order to obtain applicable properties by blending the crystalline polymer with amorphous polymer. Moreover, it is difficult to prepare high-performance engineering plastics and films showing excellent transparency simultaneously with high resistance, which, otherwise are in an inversely proportional relationship, merely by a simple physical blending process.
Due to such disadvantages of the conventional polymers, many researches and developments have been conducted continuously about novel polymers having a high glass transition temperature in combination with excellent heat resistance, mechanical properties and film formability with advanced countries as the center. Particularly, since new materials are required in various industrial fields, including flexible substrate materials for displays, solar cells and electronic paper that are key part materials of the next-generation advanced industry, as well as canopy films of combat planes and space crafts, transparent materials for space industry, or electronic and semiconductor industry, a novel polymer satisfying the above-mentioned excellent properties at the same time has been required continuously and active studies have been made about such a novel polymer.
Particularly, it is expected that the next-generation megatrend in the display, solar cell and electronic paper industry is formed largely of making ubiquitous as well as imparting flexibility and high quality image and scale-up. Therefore, it is also expected that there is a geometric increase in demand for novel transparent and highly heat resistant plastic materials suitable for such a technical megatrend.
According to such economic demand, the polyarylate-based polymer (PAR) available from Ferrania Image Technologies (Italy), cycloolefin-based polymers (COP/COC) available from Promerus (USA), polyimides (PI) available from General Electric (USA), Dupont (USA) and Mitsubishi Gas Chem (Japan), polyether sulfone polymers (PES) available from Sumitomo Bakelite (Japan) and BASF (Germany), etc. have been developed as novel materials of transparent and highly heat resistant polymeric films for flexible plastic substrates. On the other hand, in Korea, only I-Component Company has developed a film for display substrates by using an optical PES polymer available from BASF.
However, the above-mentioned novel materials of polymer films that have been developed in many countries are still insufficient to satisfy all of the technical requirements in terms of high heat resistance, mechanical properties, transparency and film formability.